1. Field of the Invention
This invention relates generally to coatings and coated articles and, more particularly, to coatings having a solar control coating with a durability-enhancing topcoat and to articles coated therewith.
2. Description of the Currently Available Technology
Solar control coatings are known for controlling the amount of solar radiation passing into buildings, vehicles, and other structures. These solar control coatings can block or reflect selected electromagnetic wavelengths and can help reduce the costs of heating and/or cooling.
Conventional solar control coatings typically include an infrared reflecting metal layer positioned between two dielectric layers. Conventional dielectric layers typically include metal oxides. A thin protective overcoat, such as titania, is deposited over the outermost dielectric layer to help protect the underlying layers from chemical and mechanical damage. Examples of known solar control coatings are disclosed in U.S. Pat. Nos. 4,610,771; 4,716,086; and 4,898,789.
Coated substrates, such as glass substrates coated with solar control coatings, can be utilized in laminated or non-laminated articles. An example of a laminated article is a conventional automotive windshield. An example of a non-laminated article is a conventional architectural window. Known solar control coatings are well suited for their intended purpose of modifying the solar control properties of the coated article.
However, conventional solar control coatings can be susceptible to mechanical or chemical damage during handling even with a conventional protective overcoat. While it would be possible to increase the mechanical and/or chemical durability of a conventional solar control coating stack by increasing the thickness of the outer protective overcoat, such an increase in thickness would also impact other parameters of the coated article, such as the reflectance, transmittance, or emissivity of the article and could significantly change the transmission characteristics, solar performance properties, and aesthetics of the coated article. This would be disadvantageous, particularly for coated glass articles destined for use in the automotive field where solar control properties, such as transmittance and/or reflectance, are controlled to meet government regulations. Additionally, increasing the thickness of the protective overcoat could also adversely impact upon the processing parameters of the coated article, such as adversely impacting the bending, annealing, tempering, or laminating processes.
Coating stacks for non-solar control purposes are known. For example, conventional camera lenses typically include an anti-reflective coating made up of a series of layers of high and low refractive index materials. These layers reduce visible light reflection when taking photographs. While these anti-reflective lens coatings are adequate for their intended purpose of reducing visible light reflection, they do not have infrared reflective metal layers and, thus, provide little or no solar control properties. While one might consider adding a conventional lens coating to a conventional solar control coating stack, such a combination would not be feasible since the resultant coating stack would not meet the optical and/or solar reflecting characteristics typically required for solar control articles, such as automotive transparencies and architectural transparencies.
Therefore, it would be advantageous to provide a coating stack having solar control properties as well as enhanced durability but without adversely impacting upon the solar control and/or aesthetic properties of the coating stack.